Method for improving the sweep of underground reservoirs by exploiting individual reservoir segments

ABSTRACT

The sweep of an underground hydrocarbon formation having reservoir segments with trapped fluids therein is increased by locating wells in individual segments and injecting extraneous fluid into the formation therefrom and producing simultaneously via other wells removed from said segments, while under the influence of an active aquifer, either native or by flooding.

United States Patent Inventors Anthony F. Altamira Houston, Tex.; JosephDaleda, Montclair, NJ Appl. No. 811,926 Filed Apr. 1, 1969 Patented Jan.12, 1971 Assignee Texaco Inc.,

New York, N.Y. a corporation of Delaware.

METHOD FOR IMPROVING THE SWEEP OF UNDERGROUND RESERVOIRS BY EXPLOITINGINDIVIDUAL RESERVOIR SEGMENTS 21 Claims, 19 Drawing Figs.

U.S. Cl 166/245,

Int. Cl E2lb 43/20 Field of Search 166/245 OTHER REFERENCES Muskat,Physical Principles of Oil Production, First Edition, McGraw-Hill BookCo., me, New York (I949), (pp. 645- 650, 677, 678 and 8 I 6- 820)Primary Examiner-Stephen J. Novosad AnomeysK. E. Kavanagh and Thomas H.Whaley ABSTRACT: The sweep of an underground hydrocarbon formationhaving reservoir segments with trapped fluids thereinis increased bylocating wells in individual segments and injecting extraneous fluidinto the formation therefrom and producing simultaneously via otherwells removed from said segments, while under the influence of an activeaquifer, either native or by flooding.

PATENTED JAN 1 2 l9?! sum 1, BF 2 METHOD FOR IMPROVING THE SWEEP OFUNDERGROUND RESERVOIRS BY EXPLOITING.

INDIVIDUAL RESERVOIRSEGMENTS CROSS REFERENCE FIELD OF INVENTION Thisinvention relates generally to the production of hydrocarbons fromunderground hydrocarbon-bearing formations, and more particularly, to amethod for increasing the sweep of hydrocarbons therefrom. Y I

BACKGROUNDOF THE INVENTION In the production of hydrocarbons frompermeable underground'hydrocarbon-bearing formations, it is customary todrill one or more boreholes or wells into the hydrocarbonbearingformation and produce hydrocarbons, such as oil, through designatedproduction wells, either by the natural formation pressure or by pumpingthe wells. Sooner or later, the flow of hydrocarbons diminished and/orceases, even though substantial quantities of hydrocarbons are still.present in the undergroundformations.

Frequently, many hydrocarbon-bearingformations are divided intoreservoir segments, each containing traps wherein hydrocarbons haveaccumulated. Thesesegments in-the underground reservoir may be caused byfaulting, permeability pinch outs,tar barriers and the like.

SUMMARY OF THE INVENTION It is an overall object of this invention toprovide an improved recovery procedure to obtain maximum sweep of asegmented reservoirinvolving a plurality of wells located strategically,viz. by having at least one well, either injection or production, incommunication with each individual reservoir segment, being under theinfluence of an active aquifer.

It is desirable that injection be initiated and continued eithersimultaneously or in turn, from wells on both-sides of thesealing faultdividing the formation into reservoir segments, when such is known toexist, until breakthrough occurs at production wells; at which timefurtherv production is discontinued and the well or. wells shut in. Inthe-absence of a native aquifer, a water drivemay be substituted.

Other objects, advantages and features of this invention will becomeapparent from a consideration of the specification withreference to thefigures in the accompanying drawing.

BRIEF DESCRIPTION OF TI-IE DRAWINGS FIG. la illustrates thesweep atbreakthrough when the in-:

fromanadditional .well as developed from the situation as disclosed inFIG. la; l

1c illustrates the final step when the second well is converted fromproduction to injection and the other well penetrating into anindividual segment is put on production;

FIG.-.2q illustrates the sweep obtained when the production wellexploiting a reservoir having segmentsdefined by a sealing fault islocated away from .the injection well behind the by model study when thewell at- A is produced to 'f onv thesame side of the sealing fault asthe injection well atx' fault; FIG. 2b illustrates the. sweep when anadditional production well is placed in operation on the'near side ofthe fault with respect't'o the injection well, as a modification of FIG.2a,-

FIGHZc'iIIustrates the'finalstep' when the functions'of the severalwells are changed to, achieve a greater sweep;

FIG. 3a illustrates the sweep when the production wells opposite thewells penetrating the formation on either side of a fault are producedconcurrently till individual breakthrough;

FIG. 3!: discloses the sweep achieved when production is continued tillbreakthrough at both production wells;

FIG. 3c corresponds to FIG. 2c illustrating the final step to achieve agreater sweep;

FIG. 4a discloses the first step of an areal sweep when both wellspenetrating the segments divided by a fault are injection wells and oneof the oppositely located wells is put on production;

FIG. 4b illustrates the step following when the production well atbreakthrough is shut in and the other oppositely located well is put onproduction;

FIG. 4c shows an alternative second step'of the sweep following FIG. 4awherein the production well at breakthrough is converted to an injectionwell, the other well located opposite the original injection wells isput on production and the injection well nearest thereto is shut in;

FIG. 4d is another alternative second step following FIG; 40' whereinboth of the original injection wells are shut in, the originalproduction well is converted to an injection well and the remaining wellis put on production till breakthrough;

FIG. 5a illustrates the sweep when the injection wells penetrating thesegments separated by the fault operate simultaneously and the pair ofproduction wells also operate simul taneously;

FIG. 5b is the converse of FIG. 5a with respect to the operatingfunctions of the wells; J

FIGS. and 6b illustrate the steps when the injection wells are locatedopposite those penetrating the segments divided by the fault, the formerfigure being the first step of the sweep and the latter FIG., theconcluding step; and

FIGS; and 7!: illustrate the steps taken to complete a sweep when ablocking fault is encountered in an inverted nine-spot pattern.

The objects of the invention are achieved by the use of production wellsin combination with injection wells which are" separated from each otherby a sealing fault and have more or less direct communication with theproduction wells.

The specification and the FIGS. of the drawings schemati cally'discloseand illustrate the practice and the advantages of ing two equal segmentscaused by a sealing faultI-The model studies indicate a sweep obtainedin an ideal" reservo' although the recovery by an actual sweep of aparticular'field' may be greater or less, depending on field parametersThe results to be described were. based on the follo of experimentalconditionsand'assumptionsi'fll'lh ran total fluid production ratesbetween wells is consta'n'tfo'r given phase or step in the production"plan; I

(2) The total amount of fluid injected is equal to the ar'iiouiit' offluid produced;

3 11: mobility ratio of the displacing todis'plaeed mildew (4) Thepermeability and thickness of the uniform; and

(5) Gravitationaleffects are not considered;

"Throughout the figures of the drawings, the

will be maintained as-follows:

. The solid circle indicates a production well, the crease cle indicatesa shut in well, an open circle a well site, arrowed open circleindicates an injection well. V

Referring to FIG. la, there is illustrated the sweepobt'aihdbreakthrough, this production well being located oppos for theextraneousdriving fluid. The sweep area amountsto 54.9 percent.

In FIG. lb, there is illustrated the increased sweep when the otheroppositely located well is put on production; the original productionwell being shut in, to result in a sweep of 73.9 percent.

FIG. lc illustrates a sweep of 83.3 percent when the second productionwell is converted to an injection well and the other well penetratingthe separated segment is put on production till breakthrough.

FIG. 2 2a illustrates the sweep obtained in the model used in FIG. whenproduction is initiated and maintained at B, located above the sealingfault and the injection well at x, until breakthrough, resulting in aswept area of 62.3 percent.

In FIG. 2b, the sweep has been raised somewhat to 68.7 percent, afterwell B is shut in after breakthrough, by initiating and maintainingproduction at well A, located on the near side of the sealing fault andthe injection well at x, until breakthrough thereat.

In FIG. 2c, the sweep has been increased to 80.9 percent when theproduction well at A in FIG. 2b is shut in and the previously shut inwell at B is converted to an injection well, and the other well at y,penetrate the separated segment, is put on production till breakthrough.

In FIG. 3a, there is illustrated the sweep in the same reservoir modelas in FIG. la when both production wells A'and B, located opposite thewells penetrating the segments divided by the sealing fault are producedconcurrently at equal rate with the injection well at x, until thedriving fluid breaks through at well A. In the second phase, asillustrated in FIG. 3b, the production well A is shown as shut in, andwell His produced until breakthrough of the injection fluid, the sweepbeing increased to 72.8 percent.

In FIG. 30, corresponding to the situation in FIG. 2c,"the lastproduction well is converted to an injection well and the wellpenetrating the other separated segment is put in production tillbreakthrough, to attain a sweep of 82.3 percent.

In FIGS. 40 and 4b, both the wells at and y penetrating the dividedsegments function as injection wells. In the former FIG., production ismaintained at A till breakthrough to attain a sweep of 79.5 percent. Inthe latter FIG., a sweepof 88.6 percent is achieved when the formerproduction well at A is shut in at breakthrough and the other well at Bopposite the in jection wells is put on production till breakthrough.

In FIG. 4d there is illustrated a sweep of 91.1 percent when thefunctions of the wells shown in FIG. 4a are changed so that x and y areshut in, the production well at A is converted to an injection well, andthe well at B is put on production till breakthrough.

FIG. 4c is a modification of the conditions of FIG. 4a, achieving asweep of 90.0 percent, when the injection well at y is shut in and thecloser well opposite thereto is put on production till breakthrough, theoriginal production well being converted to an injection well.

FIGS. 5a and 5b are converse disclosures. In the former FIG., the wellspenetrating the separated segments are injection wells at x and y, andthe wells located opposite at A and B are production wells, operatingtill breakthrough to attain a sweep of 84.4 percent.

In FIG. 5b, the wells penetrating the separated segments at x and y areproduction wells, and the wells located opposite at A and B areinjection wells. This situation results in a sweep of 87.2 percent.

FIG. 6a is the converse of FIG. 4a, with the injection wells at A and Bbeing located opposite the wells at x and y penetrating the separatedsegments, with production at x alone, to achieve a sweep of 66.4percent. Upon breakthrough and shut in at x, production is initiated andmaintained till breakthrough at y to achieve a sweep of 84.9 percent.

FIGS. 7a and 7!; illustrate the application of the invention to aninverted nine-spot pattern having a sealing fault located between thecentral injection well and a side production well.

In FIG. 7a, following production and shut in at the side wells of thepattern following breakthrough except at P,, production is maintained atthe comer wells, P, till breakthrough thereat.

In FIG. 7b, all wells suffering breakthrough are shut in, injection isshown maintained at the central. well, P (although it could be shut in)and production maintained at P, until breakthrough to achieve a greatersweep than in FIG. 7a.

Throughout the experiments. the flow of fluid through a reservoir systemis governed by Darcy's Law and is assumed to be sufficiently slow forthe inertia forces to be negligible (i.e. Stokes flow, with low Reynoldsnumber), and therefore is in the direction toward decreasing pressureand proportional to the pressure gradient.

The advantages of the method disclosed above are evident. More reservoirfluids are recovered prior to breakthrough of injection fluid, and somore ultimate recovery is obtained as compared with other productionmethods.

Although this disclosure has illustrated the practice of this inventionpractice of this invention as directed to a secondary recoveryoperation, particularly employing driving displacement fluid, theadvantages obtainable in the practice of this invention may be realizedin primary hydrocarbon production wherein the location of the sealingfault is known in order that additional production wells may beemployed.

We claim:

1. A method of producing formation fluids including hydrocarbons from anunderground hydrocarbon-bearing formation divided into segmentscontaining trapped fluids which comprises penetrating said formationwith a first pair of wells in communication with individual segments anda second pair of wells offset in corresponding positions therefrom,injecting an extraneous fluid into said formation with said segments viaa well in communication with one of said segments to displace fluidsincluding hydrocarbons in said fonnation toward one of said second pairof wells, producing said fluids including hydrocarbons from saidformation via said last mentioned well until said extraneous fluid isproduced along with said formation fluids thereat, and initiating andmaintaining producing fluids including hydrocarbons from said formationvia the other of said second pair of wells while maintaining injectingextraneous fluid into said fonnation via the injection well.

2. In the method of producing formation fluids including hydrocarbons asdefined in claim I, the first production well being closed in uponbreakthrough of said extraneous fluid.

3. In the method of producing formation fluids including hydrocarbons asdefined in claim 2, said first production well being closer to saidinjection well than the other of said second pair of wells.

4. In a method of producing formation fluids including hydrocarbons asdefined in claim 3, said first production well being further from saidinjection well than the other of said second pair of wells.

5. In the method of producing formation fluids including hydrocarbons asdefined in claim 2, the other of said second pair of wells beingconverted from a production well to an injection well upon breakthroughof said extraneous fluid, and thereupon initiating and maintainingproducing formation fluids from the other of said first pair of wellswhile injecting extraneous fluid into said formation via the convertedwell until breakthrough thereof at the last mentioned production well.

6. In the method of producing fonnation fluids including hydrocarbons asdefined in claim 1, initiating and maintaining producing formationfluids via said second pair of wells concurrently until breakthrough ofsaid extraneous fluid at one of these production wells while continuingproducing said fluids from the other production well until breakthroughthereat and thereupon converting from production to injection.

7. In the method of producing formation fluids including hydrocarbons asdefined in claim 6, initiating and maintaining producing fluids from theother of said first pair of wells and injecting extraneous fluid via theconverted injection well.

8. In the method of producing formation fluids including hydrocarbons asdefined in claim 7, producing said formation fluids being discontinuedupon breakthrough of said extraneous fluid at the production wells.

claim. 7, producing formation fluids via theproduction wells until allthe production thereof comprises said extraneous fluid. j

g 10. In the in claim 1, injecting extraneous-fluidxinto said formationvia said first pair of wells. I

11. In the method of producing formation fluids as defined in claim 10,converting the production well of said second pair of wells to aninjection well upon breakthrough of said extraneous fluid thereat andinjecting extraneous fluid into said formation therefrom untilbreakthrough thereof occurs at the other of said second pair of wells.

12. In the method of producing formation fluids as defined in claim 10,concurrently initiating and maintaining producing formation fluids viasaid second pairof wells.

13. In the method of producing formation fluids including hydrocarbonsas defined in claim 1, said .extraneous fluid being an aqueous fluid.

14. In the method of producing formation fluids including hydrocarbonsas. defined in claim 1, said extraneous fluid being a gas.' x i 15. Amethod of producing formation fluids including hydrocarbons from anunderground hydrocarbon-bearing formation divided into segments by asealing fault and. containing trapped fluids which comprises penetratingsaid formation with two pairs of paired wells, with a pair of offsetproduction wells in communication with individual segments, injecting anextraneous fluid into said'formation with said segments via the otherpair of said paired wells to displace fluids including hydrocarbons insaid formation toward said production wells,

method of producing formation fluids as defined producing said fluidsincluding hydrocarbons from said formation via one of said pair ofproduction wells until said extraneous fluid is produced along with saidformation fluids thereat, and maintaining producing fluids includinghydrocarbons from said formation via'the other of said pair ofproduction wells while maintaining injecting extraneous fluid into saidformation via the injection wells.

16. In the method of producing formation fluids including hydrocarbonsas defined in claim 15, concurrently initiating and maintainingproducing formationfluids from said formation via said pair ofproduction wells until breakthrough of said extraneous fluid thereat.

17. In the method of producing formation fluids including hydrocarbonsas defined in claim 16,-producing said formation fluids via saidproduction wells being discontinued upon breakthroughof said extraneousfluid thereat.

18. In the method of producing hydrocarbons as defined in claim 16,producing formation fluids via said production wells until all theproduction thereof comprises said extraneous fluid.

19. In the method of producing formation fluids including hydrocarbonsas defined in claim 15, said extraneous fluid being an aqueous fluid.

20. In the method of producing formation fluids including hydrocarbonsas defined in claim 15, said extraneous fluid being a gas.

21. In the method of producing formation fluids including hydrocarbonsas defined in claim 1, the pairs of wells comprising part of an invertednine-spot pattern.

2. In the method of producing formation fluids including hydrocarbons as defined in claim 1, the first production well being closed in upon breakthrough of said extraneous fluid.
 3. In the method of producing formation fluids including hydrocarbons as defined in claim 2, said first production well being closer to said injection well than the other of said second Pair of wells.
 4. In a method of producing formation fluids including hydrocarbons as defined in claim 3, said first production well being further from said injection well than the other of said second pair of wells.
 5. In the method of producing formation fluids including hydrocarbons as defined in claim 2, the other of said second pair of wells being converted from a production well to an injection well upon breakthrough of said extraneous fluid, and thereupon initiating and maintaining producing formation fluids from the other of said first pair of wells while injecting extraneous fluid into said formation via the converted well until breakthrough thereof at the last mentioned production well.
 6. In the method of producing formation fluids including hydrocarbons as defined in claim 1, initiating and maintaining producing formation fluids via said second pair of wells concurrently until breakthrough of said extraneous fluid at one of these production wells while continuing producing said fluids from the other production well until breakthrough thereat and thereupon converting from production to injection.
 7. In the method of producing formation fluids including hydrocarbons as defined in claim 6, initiating and maintaining producing fluids from the other of said first pair of wells and injecting extraneous fluid via the converted injection well.
 8. In the method of producing formation fluids including hydrocarbons as defined in claim 7, producing said formation fluids being discontinued upon breakthrough of said extraneous fluid at the production wells.
 9. In the method of producing formation fluids as defined in claim 7, producing formation fluids via the production wells until all the production thereof comprises said extraneous fluid.
 10. In the method of producing formation fluids as defined in claim 1, injecting extraneous fluid into said formation via said first pair of wells.
 11. In the method of producing formation fluids as defined in claim 10, converting the production well of said second pair of wells to an injection well upon breakthrough of said extraneous fluid thereat and injecting extraneous fluid into said formation therefrom until breakthrough thereof occurs at the other of said second pair of wells.
 12. In the method of producing formation fluids as defined in claim 10, concurrently initiating and maintaining producing formation fluids via said second pair of wells.
 13. In the method of producing formation fluids including hydrocarbons as defined in claim 1, said extraneous fluid being an aqueous fluid.
 14. In the method of producing formation fluids including hydrocarbons as defined in claim 1, said extraneous fluid being a gas.
 15. A method of producing formation fluids including hydrocarbons from an underground hydrocarbon-bearing formation divided into segments by a sealing fault and containing trapped fluids which comprises penetrating said formation with two pairs of paired wells, with a pair of offset production wells in communication with individual segments, injecting an extraneous fluid into said formation with said segments via the other pair of said paired wells to displace fluids including hydrocarbons in said formation toward said production wells, producing said fluids including hydrocarbons from said formation via one of said pair of production wells until said extraneous fluid is produced along with said formation fluids thereat, and maintaining producing fluids including hydrocarbons from said formation via the other of said pair of production wells while maintaining injecting extraneous fluid into said formation via the injection wells.
 16. In the method of producing formation fluids including hydrocarbons as defined in claim 15, concurrently initiating and maintaining producing formation fluids from said formation via said pair of production wells until breakthrough of said extraneous fluid thereat.
 17. In the method of producing formation fluids including hydrocarbons as defined in claim 16, Producing said formation fluids via said production wells being discontinued upon breakthrough of said extraneous fluid thereat.
 18. In the method of producing hydrocarbons as defined in claim 16, producing formation fluids via said production wells until all the production thereof comprises said extraneous fluid.
 19. In the method of producing formation fluids including hydrocarbons as defined in claim 15, said extraneous fluid being an aqueous fluid.
 20. In the method of producing formation fluids including hydrocarbons as defined in claim 15, said extraneous fluid being a gas.
 21. In the method of producing formation fluids including hydrocarbons as defined in claim 1, the pairs of wells comprising part of an inverted nine-spot pattern. 